Bandmill strain system

ABSTRACT

A bandmill in which a bandsaw extending around two bandwheels is subjected to strain by causing the two wheels to be spread apart by a jacking system incorporating an air spring. The air spring comprises a bellows unit or a rolling diaphragm air cylinder unit and may act through a linkage or directly between the frame of the bandmill and the journal of one of the wheels movable in the frame.

United States Patent Weavell et a1.

[4 1 Sept. 16, 1975 BANDMILL STRAIN SYSTEM Inventors: Jack Weavell, New Westminster;

James H. Porter, North Vancouver, both of Canada Assignee: CAE Machinery Ltd., Vancouver,

Canada Filed: Mar. 7, 1973 Appl. No.: 338,895

US. Cl. 83/819; 267/122; 83/818 Int. Cl. B27B 13/08; B26D l/46;

B23D 55/10 Field of Search 83/818, 819, 816; 267/122 References Cited UNITED STATES PATENTS H1895 Hanson 83/818 8/1905 Cleveland 83/819 879,500 2/1908 Stevens 83/818 2,729,003 l/1956 Cohn et al. 267/122 2,973,015 2/1961 Thompson... 267/122 X 3,810,409 5/1974 Allen et a1. 83/819 Primary Examiner-Donald R. Schran Attorney, Agent, or FirmFetherstonhaugh & Co.

[ ABSTRACT A bandmill in which a bandsaw extending around two bandwheels is subjected to strain by causing the two wheels to be spread apart by a jacking system incorporating an air spring. The air spring comprises a bellows unit or a rolling diaphragm air cylinder unit and may act through a linkage or directly between the frame of the bandmill and the journal of one of the wheels movable in the frame.

14 Claims, 7 Drawing Figures BANDMILL STRAIN SYSTEM The invention relates to bandmills and in particular to an improved jacking system for applying strain to a band saw received on the bandwheels of the mill.

Strain is conventionally applied to a bandsaw in a bandmill by a mechanical jacking system which causes the idler and driven wheels of the mill to be separated. The jacking system normally incorporates a pair of opposed and offset knife edges which engage in corresponding offset recesses in a torque bar which is biased to rotate so as to apply strain by a weight acting through a lever. Such a system enables relatively constant saw tension to be maintained on the saw blade regardless of saw length changes caused by load and temperature variations. A typical bandmill utilizing such a system is described in US. Pat. No. 3,158,184.

Recently however there has been a tendency to reduce the thickness of the saw blade in bandmills in order to in turn reduce the thickness of the cut and minimize sawdust loss. This however gives rise to instability in the blade, particularly when a log first contacts and finally leaves the saw, resulting from the rapid load changes in the thinnerand more flexible blade. Thus, the sudden load applied to the blade at the beginning of a cut tends to momentarily slow the blade down and thus the driving band wheel. Since the wheel is of heavy construction in order to provide flywheel effect and maintain speed, the shock is taken directly by the saw blade in which the tension is increased between the log and the driven wheel. This tension will cause the saw blade to stretch, and if the idler wheel is rigid and not free to move upwards, a surplus length of saw blade will exist between the log and the idler wheel thus creating a ripple or wave in the saw blade. The resulting change in length rippling effect and vibrations results in poor cutting accuracy which to a large extent negates the advantages resulting from the use of the thinner blade. Furthermore, the mechanical jacking systems above referred to are not sufficiently responsive to such rapid changes in the load on the blade and do not provide an adequate compensatory effect.

It is among the objects of the present invention to provide an improved system fir applying strain to a bandsaw, whereby the desirable high strain can be applied and maintained and which at the same time responds sufficiently rapidly to shock loadings on the saw blade to overcome the instability above referred to.

The invention therefore provides a bandmill comprising a frame, first and second bandwheels for receiving and guiding a bandsaw, first and second pairs of journals respectively journalling said first and second bandwheels, means fixedly mounting said first pair of journals in said frame, jacking means supporting said second pair of journals from said frame for varying the spacing of said first and second pairs of journals, said jacking means comprising a pair of jacks each independently supporting one each of said second pair of journals and at least one air spring for generating live strain in a bandsaw received on said bandwheels subsequent to the application of primary strain by operation of said jacks.

In a preferred embodiment, the air spring comprises a bellows which may be connected to a pressurized air reservoir. The air spring may however also comprise a rolling diaphragm air cylinder unit.

The invention will now be further described with reference to the accompanying drawings in which,

FIG. 1 is a side elevation showing the general arrangement of a bandsaw incorporating a strain system according to the invention,

FIG. 2 is a side elevation, partly in section, of one embodiment of strain system according to the invention,

FIG. 3 is a sectional plane view on the line 33 of FIG. 2,

FIG. 4 is a sectional rear elevation on the line 4-4 of FIG. 2,

FIG. 5 is a side elevation, partly in section, of a second embodiment of bandmill strain system according to the invention,

FIG. 6 is a side elevation, partly in section, of a third embodiment of bandmill strain system according to the invention and,

FIG. 7 is a plan view, partly'cut away, on the line 7-7 of FIG. 6.

Referring first to FIG. 1, this shows a bandmill having a frame 1 including a table 2. The table 2 carries a fixed lower bandsaw guide 3 and the frame 1 carries an adjustable upper bandsaw guide 4 for a bandsaw 5 extending around idler and driven bandwheels 6 and 7 respectively. The driven bandwheel 7 is mounted for rotation between a pair of journals 8, one of which is seen in FIG. 1. The idler bandwheel 6 is mounted for rotation between a pair of journals 9, one of which is seen in FIGS. 1 and 2. Each journal 9 is carried at the end of a screwed rod 10 locked in a threaded bushing l l by lock nuts 12. This arrangement permits easy and accurate alignment of the idler wheel 6 with the driven wheel 7 and the bandsaw guides 3 and 4. Accurate alignment in relation to the saw guides and driven wheel is essential for precision sawing.

The bushing 11 is pivoted at 13 at the upper end of a swan neck 14. The swan neck 14 extends upwardly from a ring boss 15 secured at the upper end of a tubular post 17. The post 17 extends slidably through guide bushings 18 provided on the frame 1 and is bolted at I the lower end to a plate 19. The plate 19 is secured by vertical spacer plates 20 to a second plate 21 mounted on a jack 22. Within the tube 17, the plate 19 carries a concave bearing plate 23 on which a convex bearing member 24 at the lower end of a strain rod 25 is received. The elements 23 and 24 constitute a rocker bearing and the clearance between the strain rod 25 and the tubular post 17 is sufficie nt to permit limited rocking movement of the strain rod.

At the upper end of the strain rod 25, an axial recess 26 is provided in which a cylindrical insert 27 is received. The insert 27 is formed with an upwardly facing knife edge 28 which engages in a downwardly facing V recess 29 formed in a torque bar 30. The journal 9 on each side of the bandmill is also provided with a recess 31 in which an insert 32 is received. The insert 32 has a concave surface against which fits a convex surface of a member 33. The member 33 has a downwardly facing knife edge 34 engaging in an upwardly facing V recess 35 formed in the torque bar 30.

The bearings 23/24 and 32/33 ensure that the load bearing knife edges self-align, provide for even distribution of load along the knife edges, and minimize friction.

Each torque bar 30 has a rocker arm 36 keyed thereto, the free end of the rocker arm 36 having one end of a link rod 37 pivoted thereto at 38, by means of self-aligning ball bushings and needle roller bearings.

As best seen in FIGS. 3 and 4, the link rods 37 on each side of the bandmill extend downwardly and are pivoted at their lower ends 39 to short levers 40, also by means of self-aligning ball bushings and needle roller bearings. Each of the levers 40 is connected to a position adjacent to one end of a cross shaft 41 which is joumalled for rotation at each end in bearings 42 carried on bracket plates 43. The bracket plates 43 are secured to the vertical plates carrying the plates 19 on each jack. In order to permit the independent raising or lowering of the jacks 22 for producing the correct tilt in the idler wheel 6, the bearings 42 incorporate selfaligning rollers to permit limited independent movement relative tothe cross shaft 41.

The bracket plates 43 have portions 44 extending upwardly and rearwardly at an angle as best seen in FIG. 2. The portions 44 are upwardly slotted from their undersides and receive in loosely interlocking engagement therewith the stepped ends 45 of a bridge member 46, as best seen in FIG. 4. The loose engagement of the ends 45 in the slots also facilitates independent operation of the jacks 22.

A lever 47 extends rearwardly from the cross shaft 41 to a position beneath the transverse beam or bridge member 46. The end of the lever 47 has a dependent pin 48 pivoted thereto at 49 and carrying a weight 50.

Between the transverse beam member 46 and the lever 47, a bellows unit 51 is secured, the unit having an inlet connector 52 connected by a pipe connection 53 to a reservoir 54 of air under pressure. The bellows unit 51 may be of any suitable kind, preferably having no static friction. The unit manufactured by the Firestone Tire and Rubber Company of Canada Limited under the trade description Airstroke has been found suitable for this duty.

The lever 47 has a mercury tilt switch 55 mounted thereon suitably connected into two warning light circuits (not shown) in a conventional manner for indicating respectively excessively high or low positions of the lever. -In order to prevent uncontrolled upward movement of the link rod 37 which would allow the torque bar to rotate anticlockwise and slacken the bandsaw, a stop 56 is provided on each swan neck 14 so as to engage the upper surface of the rocker arm 36. Damage due to over extension of the bellows unit 51 is prevented by a crossbar 57 extending beneath the lever 47 and connected at its ends by chains 58 to the transverse beam member 46.

In operation, the bellows 51 is first pressurized to a predetermined pressure calculated subsequently to provide the required live strain in the band saw blade. The two jacks 22 are next raised simultaneously until the load on the knife edges 28 and 34 act through the rocker arm 36, link rod 37 and cross shaft 41 to compress the air in the bellows 51. This jacking continues until the lever 47 is lifted from the crossbar 57 into a balanced sensitive state. This state can be determined by means of the two indicator lights (not shown) operated by the mercury tilt switch 55. The saw is then momentarily started to check that the saw is running correctly on the wheels, one or other of the jacks 22 being independently adjusted to provide correct running and the correct tooth projection. The saw is then ready for full operation.

With an arrangement generally as above described, a total strain of 24,000 pounds on a 5 foot bandmill or 65,000 pounds on a 9 foot bandmill can be developed with an air pressure not exceeding 50 pounds per square inch. By slightly increasing the air pressure, the weight 50 can be dispensed with, although it may be preferred to retain it.

Referring now to FIG. 5, this shows a bandwheel strain system generally similar to that of FIGS. 2 to 4 but modified in respect of the means of supplying air pressure. Similar features however, are accorded the same reference numerals and will not be further described.

The embodiment of FIG. 5 omits the bellows unit 51, the portions44 of the bracket plates 43 and the transverse beam member 46. The lever 47 however is further provided with an upstanding lever portion 60 to which is pivoted one end 61 of a piston rod 62 extending from an air cylinder unit 63. The other end of the air cylinder unit 63 is pivoted at 64 in a bracket 65 secured to the frame 1. The air cylinder unit 63 is preferably a rolling diaphragm air cylinder, for example of the kind manufactured and sold under the registered trade mark Bellofram". The air cylinder unit 63 is connected by means of the connection 53 44 to the air reservoir 54.

The operation of the embodiment shown in FIG. 5 will be apparent. The rotation of the cross shaft 41 is in this case caused through the lever portion 60 by pressurization of the air cylinder unit 63.

Referring now to FIGS. 6 and 7, these show a third embodiment according to the invention. The basic construction is generally similar to the assembly described with reference to FIGS. 2 to 4. The same features have been assigned the same reference numerals and will not be further described.

In this embodiment, the bellows unit 51, portions 44 of the bracket plates 43 and the transverse beam mem ber 46 are omitted, the remaining portions of the linkage previously described then serving only to ensure wheel stability and prevent sideways tilting. Weight 50 may or may not be included.

On each side of the wheel 6, the bosses 15 are provided with forwardly extending support platforms 70, the journals 9 being provided with forwardly extending reaction plates 71 immediately above the platforms 70. A bellows unit 72 is secured between each platform and the reaction plate 71 immediately above it, and has a connector 73 connected by means of an air connection 74 to an air reservoir (not shown) similar to the reservoir 54 of FIGS. 2 to 4.

In this embodiment, the strain on the bandsaw is effected simultaneously by means of the deadweight 50, when provided, acting through the linkage 47, 36 and by pressurization of the bellows units 72 to cause separation of the plates 71 from the platforms 70.

The bellows may contain an inert gas instead of air.

I claim:

1. A bandmill, comprising a frame,

- first and second bandwheels for receiving and guiding a bandsaw,

first and second pairs of journals respectively journalling said first and second bandwheels,

means fixedly mounting said first pair ofjournals in said frame, I

a pair of jacks each independently supporting one each of said second pair of journals,

a pair of torque bars each having two offset oppositely facing recesses,

. a first pair of knife edged members each mounted on one of said jacks and engaging in one recess in one of the torque bars,

a second pair of knife edged members each mounted on one of said secondjournals and engaging in the other recess in one of the torque bars,

a pair of rocker arms each secured so as to project radially from one of said torque bars for rotation therewith, i i i r a pair of bracket members mounted on and extending in parallel relation one each from each of said jacks,

a cross shaft mounted for rotation between said bracket members,

a pair of levers extending from said cross shaft adjacent each end thereof for rotation therewith a pair oflinks each connecting a rocker arm to one of said levers,

an actuating lever extending from said cross shaft at a central position,

a bridge member extending across said bracket members above said actuating lever, and

a gas spring secured between said actuating lever and said bridge member whereby pressurization of the gas spring causes simultaneous rotation of said torque bars to increase the spacing of said second journals from said jacks.

2. A bandmill as claimed in claim 1, wherein a weight is suspended from the end of the actuating lever.

3. A bandmill comprising a frame,

first and second bandwheels for receiving and guiding a bandsaw,

first and second pairs of journals respectively journalling said first and second bandwheels,

means fixedly mounting said first pair ofjournals in said frame;

supporting means for each of said second pair of journals comprising a jack spaced from the second journal,

a support on said jack and extending towards the second journal and having an end near the journal,

a torque bar between said support end and the second journal and having two offset oppositely facing recesses,

a first knife edge member mounted on the support end and engaging in one of said recesses,

a second knife edge member mounted on the second journal and engaging the other recess of the torque bar,

rocker arms secured to and radiating from the torque bar in a direction away from said support;

a common cross shaft below said rocker arms and rotatably mounted near its ends,

link means connecting each rocker arm to the cross shaft to cause said shaft to rotate when said each rocker arm moves during rotation of the torque bar connected thereto and vice versa, and

an air spring so mounted as to generate live strain in the bandsaw by resiliently urging the second journals away from the first journals,

4. A bandmill as claimed in claim 3 in which said air spring is connected to the cross shaft so as to resist rotation thereof by movement of said rocker arms.

5. A bandmill as claimed in claim 4 in which the air spring is connected to the cross shaft through a lever connected to and radiating from the latter.

6. A bandmill as claimed in claim 3 including a weight connected to the cross shaft so as to assist the air spring. i

7. A bandmill as claimed in claim 5 in which said lever is substantially parallel with said rocker arms, and said air spring is connected to said lever at a point spaced from the cross .shaft, andsaid link means are connected to the respective rocker arms at points spaced from the respective torque bars.

8. A bandmill as claimed in claim 7 in which said link means are connected to the cross shaft by levers radiating from the latter, said levers being substantially parallel to the rocker arms.

9. A bandmill as claimed in claim 7 including a weight connected to said lever at a point spaced from the cross shaft.

10. A bandmill as claimed in claim 3 including a lever connected to and radiating from the cross shaft, said lever being substantially parallel with said rocker arms, and a weight connected to said lever at a point spaced from the cross shaft.

11. A bandmill comprising a frame,

first and second bandwheels for receiving and guiding a bandsaw,

first and second pairs of journals respectively journalling said first and second bandwheels,

means fixedly mounting said first pair of journals in said frame,

jacking means supporting said second pair of journals from said frame for varying the spacing of said first and second pairs of journals, said jacking means comprising a pair of jacks each independently supporting one each of said second pair of journals,

means supporting each second journal from the corresponding jack to allow movement away from the jack,

means interposed between each second journal and the corresponding jack and operable to cause said movement,

said interposed means including a rotatable member for causing such movement,

at least one gas spring having one end fixed against movement and an opposite end so connected to the second pair of journals as to generate live strain in a bandsaw received on said bandwheels subsequent to the application of primary strain by operation of said jacks,

means associated with said gas spring and operatively connected to said interposed means for causing operation of said interposed means in response to the pressurization of said gas spring,

said means operatively connected to said interposed means comprising:

a pair of rocker arms each secured so as to project radially from one of said rotatable members for rotation therewith,

a cross shaft,

- means mounting said cross shaft between said jacks for rotation.

12. A bandmill as claimed in claim 11, wherein said gas spring comprises a bellows unit.

13. A bandmill as claimed in claim 11, wherein said means operatively connected to the interposed means further comprises a weight connected for applying a torque to said cross shaft supplemental to the torque applied by the gas spring.

14, A bandr'nill comprising a frame,

first and second bandwheels for receiving and guiding a bandsaw,

first and second pairs of journals respectively journalling said first and second bandwheels,

means fixedly mounting said first pair of journals in said frame;

a jack for each second journal,

a tubular support between each jack for the corresponding second journal,

means supporting each second journal from the corresponding tubular support to allow movement away from the latter tubular support and the jack thereof,

a strain rod supported by each jack and extending through the corresponding tubular support to near the adjacent second journal,

means interposed between each second journal and the corresponding strain rod and operable to cause said movement,

a gas spring mounted to generate live strain in the bandsaw by resiliently urging the second journals away from the first journals, and means associated with said gas spring and operatively connected to said interposed means to cause said gas spring to maintain live strain in the bandsaw and to absorb shock loads applied thereto. 

1. A bandmill, comprising - a frame, - first and second bandwheels for receiving and guiding a bandsaw, - first and second pairs of journals respectively journalling said first and second bandwheels, - means fixedly mounting said first pair of journals in said frame, - a pair of jacks each independently supporting one each of said second pair of journals, - a pair of torque bars each having two offset oppositely facing recesses, - a first pair of knife edged members each mounted on one of said jacks and engaging in one recess in one of the torque bars, - a second pair of knife edged members each mounted on one of said second journals and engaging in the other recess in one of the torque bars, - a pair of rocker arms each secured so as to project radially from one of said torque bars for rotation therewith, - a pair of bracket members mounted on and extending in parallel relation one each from each of said jacks, - a cross shaft mounted for rotation between said bracket members, - a pair of levers extending from said cross shaft adjacent each end thereof for rotation therewith - a pair of links each connecting a rocker arm to one of said levers, - an actuating lever extending from said cross shaft at a central position, - a bridge member extending across said bracket members above said actuating lever, and - a gas spring secured between said actuating lever and said bridge member whereby pressurization of the gas spring causes simultaneous rotation of said torque bars to increase the spacing of said second journals from said jacks.
 2. A bandmill as claimed in claim 1, wherein a weight is suspended from the end of the actuating lever.
 3. A bandmill comprising a frame, first and second bandwheels for receiviNg and guiding a bandsaw, first and second pairs of journals respectively journalling said first and second bandwheels, means fixedly mounting said first pair of journals in said frame; supporting means for each of said second pair of journals comprising a jack spaced from the second journal, a support on said jack and extending towards the second journal and having an end near the journal, a torque bar between said support end and the second journal and having two offset oppositely facing recesses, a first knife edge member mounted on the support end and engaging in one of said recesses, a second knife edge member mounted on the second journal and engaging the other recess of the torque bar, rocker arms secured to and radiating from the torque bar in a direction away from said support; a common cross shaft below said rocker arms and rotatably mounted near its ends, link means connecting each rocker arm to the cross shaft to cause said shaft to rotate when said each rocker arm moves during rotation of the torque bar connected thereto and vice versa, and an air spring so mounted as to generate live strain in the bandsaw by resiliently urging the second journals away from the first journals,
 4. A bandmill as claimed in claim 3 in which said air spring is connected to the cross shaft so as to resist rotation thereof by movement of said rocker arms.
 5. A bandmill as claimed in claim 4 in which the air spring is connected to the cross shaft through a lever connected to and radiating from the latter.
 6. A bandmill as claimed in claim 3 including a weight connected to the cross shaft so as to assist the air spring.
 7. A bandmill as claimed in claim 5 in which said lever is substantially parallel with said rocker arms, and said air spring is connected to said lever at a point spaced from the cross shaft, and said link means are connected to the respective rocker arms at points spaced from the respective torque bars.
 8. A bandmill as claimed in claim 7 in which said link means are connected to the cross shaft by levers radiating from the latter, said levers being substantially parallel to the rocker arms.
 9. A bandmill as claimed in claim 7 including a weight connected to said lever at a point spaced from the cross shaft.
 10. A bandmill as claimed in claim 3 including a lever connected to and radiating from the cross shaft, said lever being substantially parallel with said rocker arms, and a weight connected to said lever at a point spaced from the cross shaft.
 11. A bandmill comprising a frame, first and second bandwheels for receiving and guiding a bandsaw, first and second pairs of journals respectively journalling said first and second bandwheels, means fixedly mounting said first pair of journals in said frame, jacking means supporting said second pair of journals from said frame for varying the spacing of said first and second pairs of journals, said jacking means comprising a pair of jacks each independently supporting one each of said second pair of journals, means supporting each second journal from the corresponding jack to allow movement away from the jack, means interposed between each second journal and the corresponding jack and operable to cause said movement, said interposed means including a rotatable member for causing such movement, at least one gas spring having one end fixed against movement and an opposite end so connected to the second pair of journals as to generate live strain in a bandsaw received on said bandwheels subsequent to the application of primary strain by operation of said jacks, means associated with said gas spring and operatively connected to said interposed means for causing operation of said interposed means in response to the pressurization of said gas spring, said means operatively connected to said interposed means comprising: - a pair of rocker arms each secured so as to project radially from one Of said rotatable members for rotation therewith, - a cross shaft, - means mounting said cross shaft between said jacks for rotation.
 12. A bandmill as claimed in claim 11, wherein said gas spring comprises a bellows unit.
 13. A bandmill as claimed in claim 11, wherein said means operatively connected to the interposed means further comprises a weight connected for applying a torque to said cross shaft supplemental to the torque applied by the gas spring.
 14. A bandmill comprising a frame, first and second bandwheels for receiving and guiding a bandsaw, first and second pairs of journals respectively journalling said first and second bandwheels, means fixedly mounting said first pair of journals in said frame; a jack for each second journal, a tubular support between each jack for the corresponding second journal, means supporting each second journal from the corresponding tubular support to allow movement away from the latter tubular support and the jack thereof, a strain rod supported by each jack and extending through the corresponding tubular support to near the adjacent second journal, means interposed between each second journal and the corresponding strain rod and operable to cause said movement, a gas spring mounted to generate live strain in the bandsaw by resiliently urging the second journals away from the first journals, and means associated with said gas spring and operatively connected to said interposed means to cause said gas spring to maintain live strain in the bandsaw and to absorb shock loads applied thereto. 